Photoresist compositions are used for the formation of circuit patterns such as circuits of liquid crystal display devices or semiconductor integrated circuits. Conventionally, novolak-based resins which are alkai-soluble phenol-(or cresol-) formaldehyde resins, and naphthoquinonediazido-based compounds as photosensitive materials are widely used in photoresist compositions, as disclosed in U.S. Pat. Nos. 3,666,473, 4,115,128, and 4,173,470.
Recently, along with increasing requirements of fine micro-circuit patterns, the wavelengths of KrF (248 nm) and ArF excimer laser (193 nm) are used for the formation of circuit patterns. At these wavelengths the novolak-based resins and naphthoquinonediazo-based compounds lose their applicability due to their poor sensitivity and strong absorption at 248 and 193 nm. Consequently, there is a demand for the development of a novel photoresist resin that can be used effectively at the above wavelengths.
It is essential for a novel photoresist resin to satisfy various requirements such as high sensitivity, high resolution, and high resistance against dry etching. Among those requirements, sensitivity is the most important property. As a solution to enhance sensitivity, the concept of chemical amplification has been introduced in this field of technology.
In the chemical amplification process, an active species generated by a photochemical reaction acts as a catalyst which promotes a continuous reaction of deprotection, crosslinking, and the like. As a result, the total quantum yield is amplified to a much higher level with a small amount of the active species. In this manner, a highly-sensitive photoresist is provided. Recently, chemically amplified photoresists have been increasingly highlighted in photolithographic processes for semiconductor production in order to achieve high photosensitivity. Chemically amplified photoresist compositions contain photoresist resins having acid-sensitive reactivity, photoacid generators, and organic solvents as a mixing medium for other components.
The reaction mechanism of chemically amplified photoresists is such that photoacid generators generate strong protonic acids when they are exposed to light and these acids cause an acid-catalysis reaction of the photoresist resins to proceed. At this stage, a deprotection reaction is preformed for a positive photoresist composition, whereas a crosslinking reaction is performed in the case of a negative photoresist. As a result of such a reaction, the exposed portion shows a different solubility in a developing agent than the unexposed portion, and can be utilized in patterning process. As an example of these chemically amplified photoresists, a compound of polyvinylphenol resin protected by a t-butoxycarbonyl group-photoacid generator is disclosed in U.S. Pat. Nos. 4,311,782, 4,405,708, and 4,491,628. The ArF excimer laser lithography is expected to be the most promising lithography method for manufacturing of 1 Gbit or more DRAMs of semiconductor chips. However, since aromatic compounds in the polyvinylphenol give low photosensitivity due to strong absorption at a wavelength of 193 nm, it is only applicable at a wavelength of 248 nm or higher.
Under these circumstances, in order to develop a photoresist resin having high transmittance at a wavelength of 193 nm, and with high resolution as well as high resistance against dry etching, an aliphatic cyclic compound-included chemically amplified photoresist has been considered. For example, there has been reported in U.S. Pat. Nos. 5,585,223, 5,691,111, and 5,756,850 a compound with an alicyclic compound bonded on a (meth)acrylic side chain or a (meth)acrylic polymer having an alicyclic compound as a dissolution inhibitor. Another type of compound with an alicyclic compound composed of a polymeric main chain by means of copolymerization of norbornene monomers and maleic anhydride has also been reported in U.S. Pat. No. 6,028,153.
For a chemically amplified negative photoresist using a photoacid generator, U.S. Pat. Nos. 6,106,998, 6,074,801, and 5,955,241 disclose a process using an epoxy group or an alkoxymethylamide group as a crosslinking functional group. However, there is still an unsatisfactory level of resolution due to the occurrence of swelling during the developing process.